1. Field of the Invention
The present invention generally relates to the field of stone surface plates and machine bases and to methods and apparatus for reinforcing natural stone for providing dimensionally stable and less vibration prone stone surface plates and machine bases. More specifically, natural stone is reinforced by boring long, small diameter holes in a stone plate and inserting a tendon in each hole which is then placed in tension by jacking and retained by plural end fasteners engageable with opposite surfaces of the stone so as to place desired portions of the stone in compression. The term "surface plate" as used herein refers to a stone slab or plate having at least one precisely ground work surface (usually an upper surface) which is normally used as a support for other equipment such as sensitive measuring devices, optical comparaters and lens grinders. The term "machine base" as used herein refers to large stone supports for machines which usually include one or more ground surfaces. The generic term "stone formed work support" is used herein to refer to surface plates, machine bases and the like.
2. Related Art
Certain precision machine tools and other apparatus require a strong, stable, vibration-free and dimensionally stable mounting support for optimum operation. In the past, natural stone plates have provided the most stable support for such devices.
Unfortunately, natural stone is somewhat limited in use due to its inherent mechanical properties. For example, typical stone such as Barre granite native to Vermont has a low modulus of elasticity and low modulus of rupture. Consequently such granite is brittle and will easily fracture. The low modulus of rupture necessitates that stone plates used as machine bases be thick and span only short distances.
Stone bases as presently used have a low first bending mode frequency and are therefore susceptible to low frequency resonant vibrations caused by the fact that many of the machines and devices which they support generate such low frequencies. The present invention increases the first bending mode frequency so as to minimize resonant frequencies generated in the stone.
It is also known that micro-cracks can cause stress to focus in a small region of the stone, resulting in increased possibility of additional extensive cracking and possible fracture and even failure cracking under load-induced stress. Such failure in stone used to support sensitive equipment can at worst damage or destroy the equipment or impair or prevent its operation.
Another problem with prior known stone formed work supports is that they deflect when placed under heavy load and are consequently not usable for supporting a wide variety of items of different weights due to different amounts of deflection under different loads.
Therefore, there has been a long-existing need to provide stone surface plates having greater strength and rigidity.
Another problem encountered in providing stone bases or supports for machinery or equipment arises from the fact that the support portions of the machinery engaging the stone may be widely spaced and/or at different elevations so that fabrication from a single unitary stone workpiece to accommodate the geometry of the item to be supported is difficult, expensive and sometimes impossible.
It has been conventional practice in the past to embed metal reinforcement rods and the like in cement or concrete prior to setting as shown in U.S. Pat. Nos. 313,019; 627,424; 744,056; 813,872; and 1,951,132. It has also been known to use reinforcement rods embedded in concrete to connect plural blocks together as shown in U.S. Pat. No. 627,424. However, the use of such connections has not employed high tension rods which operate to compress the connected members to increase their strength.
It has also been conventional practice to use threaded rods such as those manufactured by Dywidag Systems of New Jersey, U.S.A., which are tensioned by jacking and retained by rotary nuts threaded onto the rods in concrete construction. Post-tensioned concrete beams and columns have also been employed in building construction in conjunction with concrete beams, columns, and slabs that have been pre-tensioned. Prestressed anchors have also been used in stabilization of dams, retaining walls, underground excavations and the like. However, none of the above-noted prior art practices teaches or suggests the present invention's use of stone compression for solving the aforementioned problems of the stone formed work support specifically with regard to the modulus of elasticity increase.